1. Field of the Invention
This disclosure is directed toward field emission surfaces, and is more particularly directed toward improvements in cold, low field, high current, low noise field emission devices and surfaces. Such devices are used in field emission display devices such as video displays and information displays.
2. Background of the Art
U.S. Pat. No. 4,663,559 and E.P.S. 0,228,616 B1, both to Alton O. Christensen (Christensen), disclose a field emission device which produces high current, low noise, low lateral energy, stochastic electron emission from a multiplicity of insulative particles subject to a field. The insulative particles are in and of a surface thickness comprised of a random mixture of insulative and conductive particles. Emission is achieved at applied potentials of about 5 volts which produce a field sufficient to emit electron currents of nanoamperes to milliamperes. Single devices or arrays of devices may be batch fabricated. Each device has an integral, implicitly self-aligned electron optic system comprising means for modulating, focusing and deflecting the formed current beam, and means for shielding the device from ambient magnetic fields.
The Institute of Electrical and Electronic Engineers (IEEE) sponsored annual International Vacuum Microelectronics Conference Proceedings, as well as many other publications in the art, are replete with many field emission materials, devices, and fabrication techniques. Worldwide field emitter development is recognized as having been fostered by the work of Spindt as disclosed in U.S. Pat. No. 3,755,704 as supported by Gray of NRL. Emphasis in the field, as reflected in recent conferences devoted to the technology, has been directed toward field emitters for excitation of phosphors to make information and video display products. Emission characteristics have been published for a wide variety of metals and metal compounds, such as borides, carbides, and nitrides. Field emission displays have been demonstrated, for example, by Coloray Inc., SRI, and PixTech Inc. using gated, pointy molybdenum metal emitters. Other developers have demonstrated field emission displays using pointy silicon emitters. SI Diamond, Inc. has demonstrated field emission displays using diamond-like carbon surfaces.
All prior art field emitters suffer from at least three or four significant deficiencies which affect the reliability and operating life when these devices are utilized in information or video displays. These deficiencies are summarized as follows:
(a) The emission surfaces oxidize and/or are poisoned by gasses within the display, or by gases generated by a phosphor used in the display thereby limiting the operating life of the emission device. PA1 (b) The turn-on potentials and current modulating potentials are in the range of 25 to 300 volts. This range of potentials requires considerable power, dissipates considerable heat, and requires expensive high voltage control and address circuitry to operate the display device. PA1 (c) The high fields in excess of 3.times.10.sup.9 volts/meter, required for higher current emission, stress and tend to modulate the emitting surface thereby producing mechanically and temporarily unstable emission sites. This results in bursts and deficits of current from the emission sites. PA1 (d) The stochastic nature of field emission, and added burst noise, requires incorporation of high-valued resistors added in series typically with the cathode terminal of the emitter to limit noise. Such resistors increase the potential required to produce currents required to excite display phosphors. Such resistors are inadequate since they reduce the potential to the entire emission surface, and not just to the emission area affected. The parasitic capacitance of the resistors together with the high value of series resistance produces a time constant delay in action that may well limit efficacy. PA1 (a) an emission device with an emitter surface of thickness which is about the electron ballistic transport length therein, thereby providing an emission surface which is insensitive to gases that oxidize or poison the emission surface and which is not detrimental to current emission; PA1 (b) an alternate metal to Cr.sub.3 Si for the cermet of insulative particles (preferably SiO.sub.2) and conductive particles, which is preferably Al.sub.2 Li.sub.3 thereby lowering the operating potential required to operate the device such that sufficient current is emitted to activate a phosphor display; and PA1 (c) other qualified materials of characteristics similar to SiO.sub.2 to form a co-deposited, graded cermet with Cr.sub.3 Si and Al.sub.2 Li.sub.3.
An object of this invention is to provide a field emission device with an emitter surface which is insensitive to gases that oxidize or poison the emission surface. Such gases and other contaminants emanate from a phosphor when the emission device is used in phosphor display devices.
Another object of the invention is to provide a field emission device that can be operated at lower potentials thereby reducing power requirements and minimizing heat dissipation requirements.
Still another object of the invention is to provide a field emission device which is operated at lower field in order to reduce mechanically and temporarily unstable emission sites which result in current bursts and current deficits at these sites. Even at reduced operating fields, the device emits current sufficient to operate display devices.
A still further object of the invention is to provide a field emission device which incorporates internal resistors which provide series resistance to limit noise at affected emission areas thereby eliminating the need to limit noise by incorporating high-valued resistors in series typically in series with the cathode terminal of the emission device thereby reducing the potential to the entire emission surface and increasing potentials required to produce current sufficient to excite display phosphor.
There are other objects and advantages of the present invention that will become apparent in the following disclosure.